But as has often happened in 30 years of shuttle flights, Discovery still sits on launch pad 39A at the Kennedy Space Center here in Florida, waiting as mission managers worked their way through a minor helium leak, a minor electrical problem and Florida's famously unpreditable weather.

They delayed this morning for the fourth time, after they found a hydrogen leak while fueling. As they were inspecting the ship on the launch pad, they also found a 7-inch crack in the now-famous insulating foam on the shuttle's orange external fuel tank, potentially troublesome if some had fallen off and hit Discovery during liftoff.

The launch is now delayed to at least Nov. 30 at 4:05 a.m. ET. The angle of the sun on the orbiting shuttle would have prevented a launch after Monday, and there is also a Russian launch NASA needs to wait out.

"We're going to fly when we're ready, and clearly we were not ready to fly today," shuttle launch director Mike Leinbach said. "It's a machine, and every now and then machines break."

Last Liftoff for Space Shuttle Atlantis

The bigger problem is that Discovery is flying for the last time, with absolutely no consensus on what will come after the shuttles are retired next year.

Forida's weather today was sunny but gusty. The longer-range forecast for the space agency: cloudy with a chance of layoffs.

People at NASA will tell you the shuttles are magnificent machines, but they were asked to do too many things and became too complicated for their own good. NASA needed them as cargo ships, orbiting laboratories and satellite launchers. The Pentagon wanted them to be able to capture Soviet satellites. It's a little like buying a car that can deliver 40 kids to school, haul lumber, and win the Indy 500.

Flying and Floating in an F-16

"It is a vehicle the likes of which we won't see again, for probably decades if not many decades," said astronaut Michael Barratt, a Discovery crew member who has already spent 197 days orbiting in the space station. "The carrying capacity of this ship, the number of people, the fact that it can be an independent orbiting laboratory or a massive cargo hauler -- it is an incredible spaceship."

Tragically, of course, two of America's five shuttles have already been lost. Roads and buildings at NASA centers are named for the 14 astronauts who died on Challenger and Columbia.

Newsman's Wild Loop in an F-16

Put all those things together, and you understand why, since the mid-1990s -- half the length of the shuttle program -- NASA has been working on something to replace the shuttle. In 2004 the Bush administration ordered that the fleet be retired by now -- as soon as they could finish assembling the space station -- and replaced with an exploration program called Constellation.